<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <style>
        #box{width:100px;height:100px;border:1px solid #000;}
    </style>
</head>
<body>
    
    <div id="box"></div>

    <script>
        var box = document.getElementById("box");
        console.log(box);
        //console.dir(box);
        
        box.style.backgroundColor = '#f90';
    </script>
</body>
</html>